Github user fhueske commented on a diff in the pull request:
https://github.com/apache/flink/pull/4471#discussion_r132230160
--- Diff:
flink-libraries/flink-table/src/main/scala/org/apache/flink/table/plan/util/UpdatingPlanChecker.scala
---
@@ -56,17 +59,20 @@ object UpdatingPlanChecker {
}
/** Identifies unique key fields in the output of a RelNode. */
- private class UniqueKeyExtractor extends RelVisitor {
-
- var keys: Option[Array[String]] = None
+ private class UniqueKeyExtractor {
- override def visit(node: RelNode, ordinal: Int, parent: RelNode): Unit
= {
+ // visit() function will return a tuple, the first element of tuple is
the key, the second is
+ // the key's corresponding ancestor. Ancestors are used to identify
same keys, for example:
+ // select('pk as pk1, 'pk as pk2), both pk1 and pk2 have the same
ancestor, i.e., pk.
+ // A node having keys means: 1.it generates keys by itself 2.all
ancestors from it's upstream
--- End diff --
`A node can have keys if it generates the keys by itself or it forwards
keys from its input(s).`?
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